Cellular mobile radio networks which expand the telephone service of wired networks to mobile subscribers are already known in the state of the art. Telephone systems with so-called cordless telephones have great significance for use in the private sector. The generally known GSM network expands the services offered by the introduced ISDN network to the mobile areas. Said network is designed for high compatibility with the ISDN network.
The other country-wide mobile radio systems which provide an expansion to the radio area of the services offered by existing wired networks are described in more detail in the following.
Cordless telephones offer a service which is available above all in the area of the subscriber's main station. It enables the telephone terminal to be connected by radio instead of by cable to a fixed station up to 300 m outside of the building or 50 m inside of the building. To that end the fixed station and the telephone terminal as the mobile part are each equipped with a transmitting and a receiving facility. The current DECT (Digital Enhanced Cordless Telecommunications) standard describes the protocols in a cordless telecommunications system for voice and data transmission. This system is also interesting for broad application in private branch exchanges. The DECT standard does not provide for any mobility management. The subscriber is mostly supplied inside of buildings, while in multi-cell networks such as for example the GSM network, the subscribers are predominantly reached outside of buildings. Several expansion steps are known with DECT installations. There are so-called one-cell systems which cover the supply area with only one fixed station. Due to the established low transmission capacity and the high attenuation inside of buildings, one-cell systems can be imagined for private internal use in buildings.
Multi-cell systems allow using the DECT service in larger areas, such as in one or more buildings within a private company territory (from: "An Overview of Mobile Data Communications") by B. Walke et al; it+ti 5/93 Information Technology and Technical Informatics 35 (1993); p. 12 to 25).
The previously cited multicell systems however require a controller for switching the different base stations to a TK installation since, as already mentioned, no mobility management is provided by the DECT standard. Even a direct link to a network requires a line-side connected logic circuit.